Ours is a society that thrives on showing off: showing off how much money a person makes, what clothes a person wears, even showing off who one dates! Take sports stars, actors, actresses, and musicians, most live a life of luxury and live that life very publicly.
Many of these people will develop a complex in which they feel they have earned these luxuries on their own, and through their own hands they achieved their fortune. As a result, these individuals no longer see that God blessed them with their current lives and hence they are not thankful to God.
As if bragging and flaunting aren't bad enough, what comes after this is jealousy and envy. Enough becomes not enough and we begin to envy those with more than ourselves. We may create jealousy in others. Even worse, we begin to belittle others we perceive as beneath us. For example, if we purchase a new pair of Jordan's or a Coach purse, we may tell others to "check this out; I got it for $120. I'm the first person to get them. They're limited edition."
If Allah has blessed us with money, then it's understandable we purchased such an item. But we see this quite a bit in middle school students - they begin to point out - going with the shoe example - shoes and say things like "look at those shoes, they are from Pay less" or "those Nike (or Converse, etc.) are out of style; no player wears them," and they mock the student wearing those shoes.
When we make people feel bad for what they are wearing or we make them feel embarrassed, then this is a clear indication that we are in need of an ego check. Think about the many examples throughout history of people who would show off and boast and how Allah humbled them.
"The War within Our Hearts: Struggles of the Muslim Youth" - Haseeb Quadri and Sa'ad Quadri, p. 76.